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Sterile pyuria is a term used in describing a specific urine sample test result. It is used when a urine sample is negative for infectious organisms but there are more white blood cells present than usual. There are several reasons why a doctor can find sterile pyuria, and in some cases, an infectious organism may in fact be present.
One reason urine samples are taken is to diagnose infectious diseases of the urinary tract. Changes in levels of white blood cells is one indication of the presence of an infectious disease. An infection can be identified by culturing the causative microorganisms from the urine.
An official laboratory finding of sterile pyuria can have many potential causes. These range from contamination of the sample to the presence of cancers. Sterile pyuria is a relatively common laboratory result. Women who appear to have urinary tract infections are the most likely group to have sterile pyuria.
A patient who has been treated in the previous two weeks for an existing urinary tract infection may show high levels of white blood cells but an absence of microorganisms. Accidental contamination of the sample with antiseptic can kill any microorganisms present. Sometimes, vaginal white blood cells can accidentally be mixed in with the urine when sampling, resulting in a higher level of cells in the sample than normal. Occasionally, the urine may be highly dilute due to intake of lots of fluids, which reduces the levels of infectious microorganisms in the sample itself and lowers the likelihood of culture growth.
Some infectious organisms are not found through standard laboratory culture techniques. These include the sexually transmitted diseases chlamydia, gonorrhea, or trichomoniasis. If a patient has tuberculosis that affects the genitourinary tract, the analysis will not identify it.
Noninfectious diseases that can show a high white blood cell count in urine include the inflammatory conditions prostatitis, nephritis, or sarcoidosis. Cancers of the kidneys or bladder can also raise white blood cell levels. Kidney stones are another possible cause of sterile pyuria.
If a doctor suspects the sterile pyuria is caused by a disease that requires treatment, he or she may take more samples and order more tests. These tests include genital swabbing and specific culturing for sexually transmitted diseases or urine sampling and tuberculosis tests. The laboratory may also check a urine sample for the presence of other blood cells that indicate the presence of diseases such as nephritis. The sample can also be checked for the presence of antibiotics.